When it comes to electric system troubleshooting, the multimeter is your best friend. The device combines all the features of a voltmeter, ohmmeter and ammeter into one.
Before you plug in the multimeter, let’s do a quick review of some of basic electricity terms. Electricity has three basic units: voltage, current and resistance. Voltage is measured in volts, current is measured in amps, and resistance is measured in ohms. Using water flowing as an analogy, think of voltage as water pressure, current as the rate at which the water is flowing and resistance as the size of the pipe.
Turning to the multimeter itself, it consists of three parts:
Display — This is where you will see the measurements.
Knob/Dial —Use the knob/dial to select whether you are measuring voltage, current or resistance. You also use the knob/dial to select parameter ranges within each type of measurement.
Ports — This is where the test probes are plugged into the unit.
The multimeter also comes with two probes (one black and the other red). Although there is no difference between the probes other than color, the black probe (-) is connected to the COM port on the multimeter. The red probe (+) is connected to one of the unit’s other ports depending on what is being measured.
Before using the multimeter, please read the instructions that come with it. However, here are some basic tips on how to use it.
How to take measurements
To measure voltage, set the mode to V. You will need to determine if you are measuring AC or DC voltage and select the proper mode. One end of the red probe needs to be connected to the V port and the other needs to be connected to the positive side (where the current is coming from) of the component you are testing. Connect the other end of the black probe to the other side of the component being tested. Look at the display to see the reading.
To measure current, the black probe should be plugged into the COM port. The red probe should be plugged into the port labeled “A”. When measuring current you will need to “splice” the meter into the circuit. While you will not actually have to cut a wire, you will need to put the meter in series with the circuit being tested so that the current flows through the multimeter as if it is part of the circuit.
When measuring resistance, turn the selection knob to the resistance section and make sure the red probe is plugged into the proper port. Next connect the probes to the resistor leads.
Many multimeters also will allow you to test the continuity of the circuit in order to help you locate faulty wiring.
What the tests tell you
You will want to perform a voltage test on a battery when drivers complain about flickering, dim or inoperable lights. You will use the current (amp) setting to test if there is a short or pass power to a load. Use the ohms setting when troubleshooting wires and harnesses, sensors, relays and solenoids. Use the continuity test to troubleshoot cable harnesses. This test will allow you to determine if a signal is getting from point A to point B. When testing system continuity, turn off the power supply and the system.
Don’t forget about parameters
Most of the tests you will be performing with the multimeter have both a minimum and maximum range parameter setting. It is important to select the proper range so you will get a proper measurement. If you fail to select the correct measurement range, the reading will display a 1. If this occurs, reset the device to the proper measurement range. Note, some multimeters have an auto-range feature that automatically adjusts the range for the test being performed.
While at first glance a multimeter can look intimidating to use, it is fairly easy to become proficient at it in a short period of time, especially if you first read the operating instructions.
For some tips on electric circuits and using a multimeter, go to our two Qwik Tech Tips on multimeters: